Treatment of tin-plate scrap



Oct. 14, 192

R. A. HOLLAND TREATMENT OF TIN PLATE SCRAP Filed Oct. 12 1921 lww W Pov41. Mayo/W761 zA/va whether they Patented Oct. 14, 1924.

UNITED STATES ROY ALGERNON HOLLAND, OF CO'BURG, VICTORIA, AUSTRALIA.

TREATMENT or TIN-PLATE some.

Application filed October 12, 1921. Serial No. 507,330.

To all whom itmay concern: 7

Be it known that I, Ror ALGERNON HOL- LAND, residing'at 40 LouisaStreet, Coburg, in the State of Victoria, Commonwealth of Australia,have invented certain new and useful Improvements in the Treatment ofTin-Plate Scrap; and I do hereby declare the following to be a full,clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

-This invention relates to a process of detinning tin plate and refersespecially to a process for the removal and recovery of tin rom tinplate scrap obtainable from canneries and other manufactories. The ironor steel from which the tin has been removed is suitable forremanufacture as required.

Hitherto the usual method of treatment for the recovery of tin fromtin-plate scrap has been to employ electrolysis in a solution of causticsoda with cathodes of iron or the like the anode being the tin-platescrap. usually packed in irdn baskets.

The object of this invention is to provide a process of or method oftreatment whereby the tin associated with iron in tin-plate *scrap isremoved therefrom and a solution obtained thereof without the employmentof an electric current from an extraneous source, and the subsequentrecovery of the tin from the solution in metallic form.

Our process or method of treatment is based on the electro-chemicalfact, that when dissimilar metals are placed in contact in the presenceof a suitable electrolyte, galvanic currents are set up which pass fromthe electro-positive metal through the electrolyte to theelectro-negative metal, and back through the latter to the former. Thisaction occurs whether the metals are in actual contact or connected by aconductor, or are partly or wholly immersed in the electrolyte.

It is well known that the metallic elements may be arranged in anelectromotive series according to their electro-positive powers orpositivity. In this series the metals are set down in descending orderso that each metal is electro-positive to those succeeding it andelectro-negative to those preceding it. Metals occupying higherpositions will go into solution in solutions of those lower in theseries and will displace the latter and precipitate them. Moreover ametal will evolve cations or anions accord are evolved at the cathode.

ing as it is immersed in a solution of a metal situated respectivelyhigher or lower in the electromotive series. Furthermore the magnitudeof the is greater and the rate of solution faster the farther apart theselected metals are situated in the series.

In the course of our investigations, we have discovered that iftin-plate be arranged in contact with a metal situated lower in theelectromotive series than iron and tin,

and if thetin-plate and said metal be im mersed in an electrolyteconsisting of a so- *lution of caustic soda, a hydroxide of a metalsituated higher in said series than either; the tin will go intosolution and the iron will remain unaffected; We preferably employcopper as the electronegative metal on account of its convenience andcheapness, either alone "or in association with an 'oxidizing agent suchas copper oxide or the like.

In practice we form a galvanic cell or element having the. tin plate asanode, the

copper as cathode, and the caustic soda solution 'as electrolyte. Inlieu of using a cathode of copper we may use one made of carbon suitablyimpregnated-with an oxidizing agent as copper oxide. Upon the im-'mersion of the tin plate and the copper in the electrolyte an E.M.F. is'set up, and

when the-tin plate and copper are short circuited by contact a currentflows from the tin plate through the caustic soda solution to thecopper, and back through the copper to the tin plate.

If a metal goes into solution in an electrolyte and another metal is notthrown down. it is well known that hydrogen is liberated at the cathode,and oxygen, or the combining radicle of the electrolyte at the anode.

In this galvanic element hydroxyl ions are liberated at the anode, andsodium ions The hydroxyl ting up an opposing or back which hinders thegalvanic action. To obviate this we employ copper oxide as adepolarizer, which is reduced by the hydrogen ions or hydrions; atomizedcopper being formed.

At the completion of the galvanic action the iron plate will be found tohave been freed of its coating of tin and after being drained and washedis ready for remanufacture as required.

The tin having gone into solution can be obtained in the metallic formby electrolysis. For this purpose suitable electrodes of iron or steelare introduced into the solution. These electrodes are arranged to formthe cathode while the said copper plate constitutes the anode. Uponpassage of an electric current through the solution metallic tin isdeposited upon the cathode and caustic soda and copper oxide areregenerated and are ready for re-use.

It will be obvious to persons skilled in the art of electro-chemistrythat in practice to carry out the process. apparatus can be arranged ina number of ways. For simplicity and convenience the copper-plate orcathode of our galvanic element can be constructed as a vat or containerfor the electrolyte. The tin-plate scrap is placed on the bottom of thisvat and is immersed in the electrolyte. Means are provided for holdingthe depolarizing agent and also for conveniently handling the tin-platescrap.

In order that the arrangement of apparatus for efiiciently carrying outour process may be readily understood two constructions are illustratedin the accompanying drawings by way of example.

Referring now to the drawings Figure 1 is a view in perspective of a vathaving a copper lining and laterally disposed troughs accommodating adepolarizing agent.

Figure 2 is a view in perspective of a vat provided with a dippingbasket and electrode of special construction.

Figure 3 is a sectional plan view of. portion of the electrode shewn inFigure 2.

Figure 4 is a sectional perspective view of a modified form ofelectrode.

In these drawings the numeral 1 designates a vat or container which isconstructed with an outer casing 2 of iron or other suitable materialand a lining of copper sheeting 3 or the vat may be made entirely ofcopper if preferred.

In the construction shewn in Figure 1. copper troughs 4 are fixed in anyapproved way to the sides of the vat 1. These troughs 4 are packed withcopper oxide 5 and are furnished with wire mesh covers 6 below whichporous septa 7 as asbestos sheeting may be placed, if required. Themeshed covers 6 and porous septa 7 while permit ting the electrolyticsolution of caustic soda to penetrate. freely to the copper oxide, alsoserve to retain the same within the troughs 4.

In use tin-plate scrap is placed upon the copper-lined bottom of the vat1 and is submerged beneath the caustic soda solution contained therein.The tin plate being in contact with the copper-lining, galvanic actionis set up and the tin coating goes into solution as sodium stannite, thecopper oxide in the troughs 4 being at the same time reduced to metalliccopper in the manner above described.

At the completion of the galvanic action the residual iron scrap isremoved and the tin is recoveredelectrolytically. For the latter purposeelectrodes of iron may be placed in the solution in the vat 1. Currentis furnished from an outside source to the copper lining. which formsthe anode, and passes through the solution to the iron electrodes whichconstitute the cathode. Metallic tin is depositedupon the latter whichthereafter is removed and melted down and cast into ingots.synchronously with the electro-deposition of the tin the atomized copperin the troughs 4 is re-oxidized to form copper oxide. and cautic soda isregenerated. It will be readily understood that the process is cyclic,all chemical energy being regenerated and the only consumption of energybeing that required for the deposition of the tin.

A draw-off pipe 8 can be fitted to the vat 1 through which thetin-bearing solution may be run off if required. After the treatment ofa quantity of tin-plate scrap and in order to facilitate the process thetin-bearing solution may be run oil and electrolized in a separatevessel. Upon extraction of the tin-bearing solution the vat 1 can berefilled with caustic soda solution and a fresh quantity of tin-platetreated.

In order to facilitate handling. the tinplate scrap may be placed in areceptacle such as a wire mesh basket 9 constructed to fit freely in thevat 1 and provided with handles 10 for lifting purposes.

In this basket is placed an electrode 11 comprising an inner coreconsisting of a series of fluted or V-shaped strips 12 of metalliccopper having sheets 13 of porous material, as asbestos. on oppositesides thereof and coverings 14 of wire mesh or the like. Rivets 15 orlike attachment means can be employed to fix the strips 12 to the sheets13. Cleats 16 and bolts 17 passed therethrough are employed to securelyhold toggther the component parts of the electrode 1 The spaces betweenthe copper strips 12 and the asbestos sheets 13 are filled with copperoxide which constitutes the depolarizing agent already described. Barsof iron or other preferred material can be used erings if required as aprotective covering for the edges of the porous sheets'13 and outer cov14, and to prevent displacement of the strips 12 and dislodgementof thecopper oxlde. v I

A single corrugated copper sheet likewise secured by rivets or the liketo the asbestos sheets 13 can be used if preferred in lieu of saidcopper strips 12.

In the modified electrode shown in Figure 4 a flat copper plate 18 is emloyed on each side of which is arran ed an mner wire mesh or nettin 19to hold the depolarizer in position. T iscopper plate 18 and wire mesh19 are covered with porous sheets 13 and outer wire mesh covermgs 14 andare assembled and fixed together in the manner above described. i

In operationv an electrode made as described is preferably located in acentral position in the vat 1 and. the spaces on opposite sides thereofserve to'accom'modate the tin-plate. The basket 9' containing tin-platescrap and the centrally disposed electrode is fiplaced in the vat 1which is filled with so cient caustic soda solution to cover the.

tin-plate scrap. Upon contact of outer coverings 14 and the-heads of therivets galvanic actionissetup and-the tin goes into solution in themanner above described. On completion of the action the basket 9 iswithdrawn and the electrode 11 in which the copper oxide is partly orwholly reduced is taken out and placed in an electrolyzing vat.

' used as the cathode this electrolytic process the iron cathode and tcopper oxide,

The solution of sodium stannite is run through the'draw-ofi 8 intothiselectrolyzing vat into which are also put one or more electrodes ofiron. These iron electrodesare while the; electrode 11 forms the anode.through the vat meta lic tin is deposited on e atomized copper in theelectrode 11 is re-oxidized to form cop'- per oxide in the mannerpreviousl scribed. The electrode at the completlonof isre'ady-for usewith a fresh quantity of tin-platescrap as and when required. i

In the fore oing is reduced In atomized copper,

material allowing the tin-plate with the alkali metal.

.Upon passing a current it has been stated that ormlng the depolarizingagent, 7

the -primary galvanic action and that the atomized copper therebyformed-is re-oxidized in the'secondary electrolytic action. However, ifpreferred, the at the end of'the galvanic action,'caf1 be removed fromthe cathode and in anelectrolyte in direct electrical contact with ametal negative to iron and tin in association with a depolarizingsubstan whereby galvanic. action is -set up r in the removal of themetallic tin .2. A process of detinning t consisting of immersing thetin plate scrap in an electrolyte of caustic soda in electrical'contact'with a metal electro-negative to tin and iron in associationwith depolarizing copper oxide whereby galvanic action is set I up[resulting in the formation of a soluble salt of tin.

3. In a process as claimed in claim 1' characterized by the fact thatthe electrolyte consists of a solution of hydroxide of 4. In aprocess asclaimed in. claim 1 characterized by the fact thatthe cathode I ofthegalvanic cell consists of copper.

5. In a process as claimed in claim 1 characterized by 6. In anapparatus tin'scraP, a galvanic cell comprisin a vat,

having a basket or container for t c said tin scrap provided with anelectrode-consisting' of a. metal electro-negative to .tin and the factthat the depolarizf+ ing agent consists of copper oxide. for thedetinning of iron having a packing on both sides of a layer ofdepolarizing a ent.

In testimony whereo I aflix m .ROY ALGERNON HOLLAND.

Witnesses:

s WILLIAM A. ASHTOIQ',

' I G. R. CULBER signature.

